Clear air scatterers (CAS) are turbulent motions of the air associated with ever-present hydrodynamic-thermodynamic instabilities in the atmosphere. The prevalence of this phenomenon is most pronounced during time periods when the atmospheric mix ratio is low, i.e., when there is a negative gradient in the potential temperature near the ground and solar illumination is high. The clear air scatterers often have an apparent upward component of motion that causes them to appear to accelerate away from the point of observation and may contain precipitation, rainfall, sleet, snow and clouds. The clear air scatterers as well as the observed precipitation are often convected along with the vector velocity of the wind.
In order to track these phenomena, it is necessary to measure the X (East), Y (North), and Z (Up) components of the wind velocity. To accomplish this, conventional radar techniques employ four beams spread 90 degrees apart in azimuth and each tilted θ=80 degrees up from the horizontal. The Doppler velocity observed on these beams at an altitude is used to estimate the three vector components of wind speed at that altitude. In conventional wide-band (WB) frequency modulated continuous wave (FMCW) radar processing, the time dependence is integrated out of these measurements to produce an average range-velocity matrix for the observed CAS.